1. Field of the Invention
The present invention relates to an operating condition monitoring apparatus and things pertinent to the apparatus for monitoring the operating condition of one or more production apparatuses that constitute a production line.
2. Description of Background Art
In order to monitor and evaluate the operating condition of one or more pieces of production equipment, that is, one or more production apparatuses that constitute a production line, it is desired to use an appropriate evaluation index.
A known conventional index to evaluate the operating condition of equipment is overall equipment effectiveness (see, e.g., Japanese unexamined patent publication No. 2000-123085 [page 1, FIG. 1, etc.] and Japanese unexamined patent publication No. 7-105285 [page 1, FIG. 1, etc]).
The overall equipment effectiveness is an index indicating total efficiency of production equipment in a production line and given by the following formula.overall equipment effectiveness=fully productive time/load time
The load time is given by subtracting planned equipment downtime from an possible operating time. The value obtained by subtracting equipment downtime caused by breakdowns and losses in waiting for setup and adjustment from the load time is referred to as an operating time. The value obtained by subtracting equipment downtime caused by speed losses including reduced speed and temporary stops from the operating time is referred to as a net operating time. The fully productive time is given by subtracting time relating to defective losses including improper processes and yield reduction from the net operating time.
Such overall equipment effectiveness is suitable to obtain the resultant efficiency of the equipment that has actually been operated. Since a stoppage of one piece of production equipment usually causes the other pieces of equipment to stop, the values of the actually-calculated overall equipment effectiveness of one or more pieces of equipment in a production line are approximately all the same. In short, this overall equipment effectiveness indicates values close to the operation rate of the whole production line.
There is another index to evaluate the operating condition, that is operational availability (see, e.g., “Reduction of mechanical downtime and improvement of operational availability”, Koujoukanri (Factory Management), extra edition, August 2005, Vol. 51, No. 11, pp. 30 to 31). This operational availability can be expressed by the following formula.Operational availability=net operating time/(net operating time+downtime caused by the equipment itself)The operational availability is an index excluding an influence exerted by the stoppage of other pieces of equipment, more specifically, an index calculated without the downtime caused by the other pieces of equipment, and therefore is suitable to obtain efficiency of actual operation of each piece of the equipment.
With the above-mentioned overall equipment effectiveness, however, it is difficult to identify equipment to be the cause of the production line stoppage from the operating condition of the equipment.
The stoppage of a production line caused by one piece of equipment lowers the overall equipment effectiveness of every piece of equipment in the production line. Because of this, even if there is a piece of equipment having low overall equipment effectiveness, it cannot be judged whether the equipment stopped because of its own fault or because of the other piece of equipment's fault. Consequently, it is impossible to judge whether the equipment having low overall equipment effectiveness is a main factor to stop the production line.
In the case of the above-mentioned operational availability, even if the lengths of downtimes caused by the equipment itself are the same per unit time, its operational availability takes different values according to the length of downtime caused by the other equipment. Therefore, the operational availability is also not appropriate as an index to identify equipment causing the production line to stop.
For instance, where the load time is 60 minutes, the net operating time is 50 minutes, the downtime caused by the equipment itself is 10 minutes, and the downtime caused by the other equipment is 0 minutes;operational availability=50/(50+10)×100=83%.On the other hand, where the load time is 60 minutes, which is the same as the above case, the net operating time is 20 minutes, the downtime caused by the equipment itself is 10 minutes, the downtime caused by the other equipment is 30 minutes;operational availability=20/(20+10)×100=67%.
As is apparent from the above, even if the lengths of the downtimes caused by the equipment itself are the same, the operational availability takes different values under the influence of the downtime caused by the other equipment. Therefore, it is difficult to analyze to find equipment to be a factor of the production line stoppage with the use of the operational availability of each piece of equipment.